Field of the Invention
The invention relates to an electronic device and, more particularly, to an electronic device with an antenna.
Description of the Related Art
When a metal back cover is applied to a mobile phone or a tablet computer, a distance (which is, for example, larger than 5 mm) should be provided between a built-in antenna and the metal back cover. If the distance is too short, the radiation of the antenna would be affected and the efficiency of the antenna decreases. Conventionally, a slot is formed at the metal back cover for the induced current to flow along the metal back cover, and thus the current of the antenna body would not be cancelled out. However, the overall appearance of the metal back cover is affected.
An electromagnetic bandgap (EBG) structure prevents the transmission of the surface wave, and thus the electromagnetic bandgap structure is widely used in electronic device. FIG. 1 is a schematic diagram showing a conventional electromagnetic bandgap structure. As shown in FIG. 1, the electromagnetic bandgap structure includes a first conductive element 110 and a second conductive element 120 which form a two-layer structure, and the second conductive element 120 is electrically connected to the first conductive element 110 via a conductive pillar 130.
In operation, the conductive pillar of the electromagnetic bandgap structure provides an equivalent inductance, and an operating frequency of the electromagnetic bandgap structure is lowered by increasing the length of the conductive pillar. For example, when the length of the conductive pillar increases, the equivalent inductance also increases, and the operating frequency of the electromagnetic bandgap structure decreases. However, when the length of the conductive pillar increases, the height of the electromagnetic bandgap structure also increases, and thus the electromagnetic bandgap structure cannot meet the requirement of a thinner and lighter electronic device.